Lagos, Nigeria (CNN) -- Roughly 17,000 people fled their homes in eight northern Nigerian states as violence erupted after presidential elections in Africa's most populous nation, the Nigerian Red Cross said Tuesday.

The agency reported deaths but could not give an exact number. It was treating 360 people who suffered injuries, said spokesman Andronicus Adeyemo.

Incumbent President Goodluck Jonathan, who was declared the winner Monday, appealed for unity as the breadth of the unrest sounded alarms for the government.

"My brothers and sisters, we are all winners," Jonathan said in a televised address. "In this context there is no victor and no vanquished. We have demonstrated, even in our diversity, the progress of Nigeria remains paramount for all."

"For now, his continued manning of the ministry is not in the interest of the nation," Jonathan said in a statement.

Nigerians in the northern states rioted after it became apparent that Jonathan had won, charging that the elections had been rigged.

Tuesday, the government deployed the military to restive areas as strict curfews helped maintain calm. But peace was tenuous, and another round of voting is coming up in a week.

Nigeria's elections, staggered over three weeks, conclude with the vote for governors April 26.

Jonathan hails from a Christian and animist south that is rich with oil. On the streets of the northern, mainly Muslim cities, rioters shouted the name of former military ruler Gen. Muhammadu Buhari, the main opposition candidate. The results highlighted modern Nigeria's deep divide.

"I must say that this is a dastardly act (that) is not initiated by any of our supporters and therefore cannot be supported by our party," said Buhari's spokesman Yinka Odumakin. "I must emphasize that this is purely a political matter, and it should not in any way be turned into an ethnic, religious or regional one."

Nigeria's credibility was riding on the elections after a 2007 vote that was condemned for rampant vote rigging, violence, theft of ballot boxes and intimidation.

The election this year, though marred by violence and delays because of organizational failures, was considered an improvement. British Foreign Secretary William Hague hailed the vote as a "significant step forward" for Nigeria.

However, only the ruling People's Democratic Party has signed the results; representatives of the other parties refused to do so.

The Civil Society Election Situation Room observers noted a number of irregularities, including underage voting in several states, intimidation and cases of thumbprints placed on ballots.

The observers lashed out at the Independent Nigerian Election Council's management of the election and said it had been "ineffective" in its oversight function.

"The collation process seems to have been the weakest link in the election management process," the Civil Society report said. "This state of affairs raised doubts about the authenticity of some of the figures arising from this process. Further, there were allegations that, in some cases, figures may have been doctored."